Memorized the Haru Haru Yukai,
Created 5 fictional League of Legends Champions with stats, abilities, lore which are as in depth if not more so then the actual champions, working on a sixth one,
Not sure if this counts as nerdy but in my Primary School we had a chicken pen and for a while the only popular kids were the ones which knew how to interact and raise chickens and the indepth facts about all of them so 9 year old me went home and memorized over 490 different breeds of chickens, their different qualities, their history and how to raise them in one night. Needless to say I got chicken pen maintenance rights after that.
Memorized the whole Queen Mab speech from Romeo and Juliet in 1 and a half hours (double period of English and I wanted to challenge myself)